This invention relates to electric storage batteries and more particularly to batteries wherein the electrochemically active cell elements have plates enveloped in a sheath of battery separator material. Battery separator materials are well known in the art, comprise a microporous membrane, and serve to electrically isolate the electrode and counterelectrode plates from each other. Separators generally have a high degree of porosity so as not to inhibit electrolyte circulation within the battery but very small pores for suppressing plate-shorting inter-electrode dendrite growth. Some manufacturers envelope the positive, negative or both plates in a sheath of the separator material. Separator-enveloped plates reduce the likelihood for dendrite-produced, inter-electrode shorting between the lateral and bottom edges of adjacent plates (i.e. edge-shorting) and improve the handling characteristics of the plates in the plant. The sheath typically comprises two sheets of separator material (e.g. sintered PVC) joined together along the bottom and side borders and open at the top. Usually a single strip is folded in half along the bottom, and the lateral borders of the sheets heat sealed to each other to form the sheath. The plate is positioned in the sheath such that the bottom edge of the plate lies in the fold of the strip and the heat sealed lateral borders of the sheath parallel the lateral edges of the plate it envelopes.
Batteries having separator sheathed plates open at the top suffer from two problems. First, dendrites tend to grow through the open tops of the sheaths until edge-shorting occurs between the top edges of adjacent plates. Secondly, the sheaths tend to trap electrolyte therein thereby reducing electrolyte mixing and mobility within the battery which in turn reduces the effective useful capacity and life of the battery.
It is an object of the present invention to provide an electric storage battery with separator-enveloped plates having improved electrolyte mobility and a reduced tendency for inter-electrode edge-shorting. This and other objects and advantages of the present invention will become more readily apparent from the detailed description thereof which follows.